1. Technical Field
The present disclosure relates to a physical quantity detecting apparatus that detects a physical quantity, such as a temperature, and, in particular, to a physical quantity detecting apparatus that detects a physical quantity in the form of an electrical signal.
2. Related Art
It has been quite important to detect a physical quantity, such as a temperature, and to use the detection information in determining the status of a system. As an example of such a physical quantity detection, JP-A-2009-171312, for example, discloses an on-vehicle information transmission system. The on-vehicle information transmission system detects a temperature which is a physical quantity of an inverter. The on-vehicle information transmission system includes a temperature sensitive diode, a frequency conversion circuit and a photocoupler. The temperature sensitive diode is provided at an inverter to output a voltage corresponding to the temperature of the inverter. The frequency conversion circuit is connected to the temperature sensitive diode to convert the voltage outputted from the temperature sensitive diode into an AC signal having a frequency corresponding to the voltage and to output the AC signal. The photocoupler is connected to the frequency conversion circuit to convert the AC signal outputted from the frequency conversion circuit into a pulse signal and to output the pulse signal, in a state of being electrically isolated from the frequency conversion circuit.
It is desirable that the temperatures at a plurality of positions of an inverter be detected and that the occurrence of a temperature error of the inverter be determined based on a maximum temperature. When the configuration disclosed in the patent document mentioned above is used for detecting the temperatures at a plurality of positions of an inverter, not only a plurality of temperature sensitive diodes, but also a plurality of frequency conversion circuits and a plurality of photocouplers have to be provided, according to the number of positions where temperatures are detected. This raises a problem of allowing a system to have a complicated configuration and of incurring high cost for providing such a system of a complicated configuration.